1. Field of the Invention
The present invention relates to a copying machine, an image processing apparatus, an image processing system and an image processing method and more specifically to a calibration for an image outputting apparatus, such as a printer, connected through a network to the image processing system.
2. Description of the Prior Art
In recent years, a personal computer and a peripheral, such as printers, used in combination with the personal computers, have come into wide use. Under this circumstance, documents and graphic images generated on a computer can easily be output as hard copies.
As a representative configuration of such a system, that shown in FIG. 1 is known. The figure shows an outline configuration of the system in which, for example, page layout documents such as documents by desktop publishing (DTP), documents by word processor and graphic documents are made by means of a host computer 1001 and they are printed out by an image outputting apparatus 1007 such as laser beam printers, ink jet printers and the like.
In FIG. 1, denoted by 1002 is an application operating on the host computer which typically includes word processor software such as Word of Microsoft Corp. and page layout software such as PageMaker® of Adobe Systems.
Digital documents made by the software are handed over to a printer driver 1003 through an operating system (OS), not shown, in the computer. The digital document is a set of command data which normally represents, for example, figures and characters that make up data of a page. These commands are transferred to the printer driver 1003. The commands are, in many cases, written in a language system called PDL (page description language). As the representative PDLs, GDI and PS (Postscript) are known. The printer driver 1003 transfers the received PDL commands to a rasterizer 1005 in a raster image processor 1004. The rasterizer 1005 develops characters and figures represented by the PDL commands into a two-dimensional bit map image used for actual printing out by the printer. More specifically, the bit map image is an image formed by filling a two-dimensional plane with repeated one-dimensional rasters (lines). The bit map image thus developed is stored temporarily in an image memory 1006.
FIG. 2 is an illustration schematically illustrating the processing above. A document image displayed by the application 1002 on the host computer 1001 is transferred to the rasterizer 1005 as a PDL command series via the printer driver 1003. The rasterizer 1005 maps the two-dimensional bit map image 1104, 1105, and 1106 onto the image memory 1006.
The mapped image data is sent to the color printer 1007. The color printer 1007 has an image forming unit 1008, as shown in FIG. 1, such as a known electro-photographic system or ink jet system and forms a visual image on a paper to perform printing out. The image data in the image memory is transferred to the color printer in synchronism with a synchronization signal, a clock signal or a particular color component signal transfer request, all of which is not shown and is necessary to operate the image forming unit.
In the image outputting apparatus such as the printer, which is used for outputting an image in the above-described conventional system, it is known that the hue and density of a printed image may change when printing operation is performed for a long period. This is due to a change with elapsing of time in image outputting characteristics of the printer and to increased variations in respective parts composing the printer. Also, the printer generally has individuality in the above-described change in the image outputting characteristic including the cause thereof, that is, the change with elapsing of time and soon. In this case, there may be caused a problem that, for example, a plurality of printers connected to the image processing system perform printing with different hue or the like.
For example, for the printer using the electro-photographic system as the image forming unit, the electro-photographic processes which include an exposure to a laser beam for formation of a latent image on a photosensitive body, development of the latent image with a toner, transfer of the toner image onto output medium such as a paper, and fixing of the toner image on the medium by heat, are easily influenced by ambient temperature and humidity or by change with elapsing of time in components realizing the electro-photographic processes. As a result of this, a change in the amount of toner fixed on the paper is brought to cause change in the hue or density of the printed image.
It is known that such a change in the image outputting characteristic is not peculiar to the electro-photographic system but can also occur similarly with various other printing systems such as ink jet system, heat transfer system and thermo-sensitive system.
As a configuration to solve such a problem, a system shown in FIG. 3 has been known. In this system, the printer 1007 outputs a test pattern image 1201 made up of predetermined patches 1202, 1203, 1204, 1205, the density of the output test pattern image is measured, and based on the measurement, the outputting characteristic of the image forming unit is corrected. Such processing is called a calibration. The calibration process in detail will be explained below.
When the calibration is requested, the host computer 1001 sends a test pattern output command to the raster image processor 1004. Based on the command received, the raster image processor 1004 generates bit map data for outputting and sends it to the printer 1007. The printer 1007 performs printing out based on the bit map data received on an output medium such as paper. The output pattern in this system has, as indicated by a pattern 1201, patches of four toner colors, cyan (C), magenta (M), yellow (Y) and black (K), each of which has a toner adhering area rate gradually changing from 0% to 100% in eight steps. In the figure, the eight-step patches are assigned numbers from 0 to 7, and reference number 1202 represents a horizontal row of cyan patches, 1203 magenta patches, 1204 yellow patches and 1205 black patches.
The output pattern has a total of 32 patches (4 colors×8 steps), each of which is measured for density by a reflection density measuring device 1206. The measured values (density data for each patch) are sent to the host computer 1001.
The host computer 1001 compares the respective measured values with reference values for the 32 patches preliminary stored and, based on a result of the comparison, updates the content of a correction table for correcting image data of each color C, M, Y and K. The host computer then registers the updated correction table in a table conversion unit in the raster image processor. Thus, the calibration process is complete.
The table conversion unit is a correction table used by the raster image processor to correct the image data for each color when generating a bit map image. For example, when the density of a third cyan patch in the test pattern 1201 is measured and found to be lower than the reference value in the above calibration process, what the calibrated correction table does is to correct an input density value, when it is equal to the reference value corresponding to the third cyan patch, to a value higher than the reference value. This correction can make the output density characteristic of the printer closer to the reference value over the entire density range. As a result, proper printing out can be maintained with stable output density characteristic.
With the above procedure it is possible to carry out the calibration for maintaining an appropriate output density characteristic of the printer. To do so, the density measuring device as shown in FIG. 3 that measures the patches output by the printer is required.
The density measuring device used for this purpose is generally high accurate and expensive one and thus it is not realistic in view of cost to provide it on each printer. Further, there are few users who purchase such a density measuring device only for the purpose of stabilizing the output density. If the user is in a position to use the density measuring device, the user is required to perform various troublesome operations such as measuring individual patches produced by the printer in sequence and this takes much labor and time.
In the image processing system connected with the printer via network, there is another problem. That is, the user is required to start a calibration program on the host computer, perform operations associated with the calibration, move to where the printer or scanner is installed, and perform necessary operations for printing out and reading a test pattern. Further, in the image processing system connected with a plurality of printers via network, the troublesome operations described above must be performed for all the connected printers to complete the calibration and this will take huge amounts of labor and time.
As a growing number of systems in offices are operated under the networked environment, it is proposed to use not only printers but copying machines as the image outputting apparatus for the image processing system. More specifically, the copying machines are configured so that they can not only perform generally known copying functions independently of the network system but also print out image data processed by the host computer.
In view of the image processing environment described above, it is an object of the present invention to provide a copying machine, an image processing apparatus, an image processing system and an image processing method which allow easy calibration in a networked system by effectively utilizing the functions of the copying machine.